Neutrophils display potent bactericidal activity toward Actinobacillus actinomycetemcomitans (A.a.), but only in the presence of specific IgG antibody. Localized juvenile periodontitis (LJP) subjects produce substantial amounts of IgG2 antibody against this organism. The ability of IgG2 to support phagocytosis of A.a. may be limited by the capacity of phagocyte IgG Fc receptors to bind this subclass. FcgRII, the main IgG Fc receptor present on neutrophils, exhibits a genetically-defined structural polymorphism which significantly affects IgG2 binding. One allotype, which contains histidine (H) at position 131, binds IgG2 efficiently, whereas the allotype containing arginine (R) at this position does not. In the present study, working with Dr. Mark Wilson, we determined FcgRIIA allotype in two families with LJP. FcgRILA was amplified from genomic DNA by PCR, after which FcgRIIA genotype was determined using an allele-specific oligonucleotide probe assay. Severity of periodontal disease was determined by radiographic loss of alveolar bone and by probing depth. The three most severe cases of LJP exhibited the R/R genotype, as did two post-LJP patients. The other two LJP patients, presenting with a less severe form of the disease, demonstrated H/R genotypes. The remaining subject, who did not exhibit LJP, was H/R. These preliminary results suggest that increased risk for development of LJP may be due to a unique combination of production of substantial amounts of IgG2 antibodies against A .a. and a decreased frequency of expression of the H allele of FcgRIIA.